<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script !src="">
  var a = 1;
  var b = a++;
  console.log(b) //1
  b = ++a;
  console.log(b) //3

  var c = +"123A"; // + 是可以进行数据类型统一的！
  console.log(typeof (c)) // number
  console.log(c) // NaN
  console.log(c + 1) // 123 + 1 = 124   NaN  = not a number 不是一个数

  var d = +true;
  console.log(typeof (d)); // number
  console.log(d + 3); // 4

  console.log(true == 1)
  console.log(false == 0)


  var f = + undefined
  console.log(typeof (f)) // number
  console.log(f + 1) // nan

  // none is not defined
  var g = none
  // 没有任何意义！！！！
  console.log(typeof (g)) //
  console.log(g + 1) //







</script>

</body>
</html>